This thesis describes novel insights in the human immune responses to Staphylococcus aureus wall teichoic acid (WTA), a polysaccharide that is abundantly present in the bacterial cell wall. S. aureus WTA is composed of a poly-ribitolphosphate (RboP) backbone, co-decorated with D-alanine and N-acetylglucosamine (GlcNAc) residues. Three distinct WTA glycosyltransferases have been described that can modify the RboP backbone with GlcNAc in different configurations (α- or β-GlcNAc). Based on the strain-specific expression of WTA glycosyltransferases; different WTA glycosylation profiles exist, which can greatly impact host immune responses. In chapter 2, we expand on previous findings that S. aureus interacts with skin resident antigen-presenting cells, namely Langerhans cells (LCs), through the C-type lectin receptor langerin and describe the interaction between langerin and β-GlcNAc WTA expressing S. aureus. Using synthetic WTA oligomers as a novel tool to study host lectin responses to S. aureus WTA, we confirm that human langerin interacts with β-GlcNAc, but not α-GlcNAc, modifications on WTA. In chapter 3, we highlight the use of fully synthetic WTA oligomers as powerful tools to perform in-depth structure binding analysis of glycan-specific monoclonal antibodies (mAbs). We show that WTA-mAb binding and subsequent complement activation are not only affected by GlcNAc linkage type (α- or β-GlcNAc) but also by the position of the GlcNAc moiety on the WTA backbone. Chapter 4 provides an extensive overview of the antibody repertoire to the different WTA-GlcNAc modifications in healthy donors, and ICU patients with culture-confirmed S. aureus bacteremia. For the first time we report WTA-specific IgM responses in these two human cohorts. By matching the WTA glycoprofile of the infecting S. aureus isolate to WTA-specific antibody responses within individual patients, we highlight the importance of raising antibodies to all three WTA-GlcNAc modifications. In chapter 5, we describe the identification of S. aureus-specific tissue-resident memory T cells in healthy human skin. Upon activation, these cells proliferate rapidly and produce pro-inflammatory cytokines thereby possibly contributing to protective immunity during skin infection. In conclusion, the findings presented in this thesis provide novel insights in immunity against S. aureus WTA, which could contribute in the development of a future vaccine that provides protection against S. aureus infections.